All I do is mobile training. I go to my client’s location to train them, so my fees already include all of those costs and expenses associated with the traveling time. You will get many different answers here, so you will need to decide what your time is worth when going to client’s homes. You can charge them an extra 10%, 20% or more depending on those extra expenses you might have (parking or toll fees), extra gas (mileage) or by the minutes it takes you to go to the location (extra $$ for every 10,15, 20 or 30 minutes) on top of your regular rate.
I hope this helps.